1. Field of the Invention
The present invention relates to an image pickup apparatus, such as a digital camera, which has a body thereof provided with a foreign substance detecting means for detecting foreign substance attaching to an image pickup optical system, and an operation processing method for the image pickup apparatus, a program for implementing the method, and a storage medium storing the program.
2. Description of the Related Art
In a digital single-lens reflex camera with an interchangeable lens, a foreign substance like dust or dirt existing in the camera main body may move due to interchanging of the lens, driving of a mirror, or an operation of a shutter, and adhere to the surface of a cover glass of an image pickup element of an image pickup optical system or the surface of an optical low-pass filer, an infrared cut filter, or the like disposed in the vicinity of the image pickup element. If shooting is carried out without removing the attaching foreign substance, the shadow of the foreign substance is imaged onto the image pickup element together with the image of a subject and therefore it becomes impossible to carry out shooting in a satisfactory manner.
To solve such a problem, there has been proposed an image pickup apparatus in which optical filters, such as a low-pass filter and an infrared cut filter, are disposed spaced from an image pickup element, and the space formed between the optical filters and the image pickup element is hermetically sealed and hence kept clean, thereby preventing a foreign substance from entering into the vicinity of the image pickup element.
Also, Japanese Laid-Open Patent Publication (Kokai) No. 11-234543 has proposed an image pickup apparatus (video camera) that detects a stain on a taking lens using an output signal of an image pickup element. The proposed image pickup apparatus detects a stain on the taking lens by detecting a fixed low-frequency component in a moving image that is being shot.
Also, Japanese Laid-Open Patent Publication (Kokai) No. 11-249004 has proposed a detecting method and a means for correcting an output signal of an image sensor, which are for use in a case where a foreign substance attaches to an image pickup optical system adopting a phase difference detecting system that is applied to a single-lens reflex camera or the like. With the proposed detecting method and correcting means, a difference value between adjacent pixels in an output signal of the image sensor that is uniformly illuminated is integrated and foreign substance detection is carried out as to whether the obtained integral value is greater than a predetermined value. When a foreign substance is detected, sensitivity correcting data for each pixel is changed such that the output signal of the image sensor lowered in level by the foreign substance assumes a normal value.
In the case of a single-lens reflex camera for which the flange back of an interchangeable lens is fixed, however, if the image pickup element is small, it is possible to secure a required space between filters and the image pickup element. However, due to increase in the size of the image pickup element with a recent increase in the number of pixels, it becomes difficult to secure such a required space.
Further, the above-mentioned shadow of a foreign substance is blurred on the image pickup element depending on the attaching position and size of the foreign substance and the exposure value of the taking lens, so that it is difficult to grasp the adverse effect of the foreign substance. Therefore, the photographer continues shooting without recognizing attachment of the foreign substance, and after the shooting, finds the adverse effect of the foreign substance in a scene having a different shooting condition.
Therefore, there is growing necessity to detect a foreign substance that can exert an adverse effect on shooting results with ease and reliability before shooting.